The present invention relates to gear transmissions, and, more particularly, to improvements in multiple stage transmission devices having helical gearing and capable of use in the power transmissions of motorcycles, or the like.
In the prior art there are known transmission devices for four wheel vehicles in which helical gearing is used to smoothly and silently transmit rotation to a driven shaft. In such devices plural sets of gear pairs are always provided in which to mesh a fixed gear on one shaft with a loose, rotating gear on the other shaft, whereby the loose, rotating gear of an optional set can be alternately coupled to the shaft by a synchronized clutch. On the other hand, a transmission device for a motorcycle is known in which a spur gear is used as a transmission gear and a loose, rotating gear is coupled to a shaft by a meshing clutch in which the clutch is shifted by a shift fork.
While the above-mentioned transmission device for four wheel vehicles has an advantage in that the transmission is smooth and silent because of the use of helical gearing, it has the disadvantage that the synchronized clutch necessary for its use is complicated. On the other hand, while the above described transmission device for a motorcycle, because of use of a spur gear, has a tendency toward noisy operation, it has the advantage that its clutch mechanism is simple. When the advantages of both of these transmission devices are sought to be combined, a structure such as that shown in FIG. 2 results. Use of this structure, however, results in wear in the contact portions of the clutch, particularly with clutches employing a shift fork.
The present invention is intended to ameliorate this problem and to provide a transmission device which is structurally simple, yet durable.